The United States Navy (USN), major branch of the United States armed forces charged with the defense of the nation at sea, the seaborne support of the other U.S. military services, and the maintenance of security on the seas wherever the interests of the United States extend.

Flag of the United States Navy.

The Continental Navy was established by the Second Continental Congress on October 13, 1775, to supply and support the Continental Army during the American Revolution. The navy mostly preyed on British merchant shipping during the war, capturing many enemy vessels. The navy was disbanded in 1784, and until 1798 U.S. merchant ships sailed unprotected from attacks by Barbary pirates. To counter harassment by these pirates and the French, the U.S. Congress established the Department of the Navy on April 30, 1798.

The U.S. Navy fought a number of successful ship-to-ship actions in the War of 1812, which in part grew out of British impressment of American seamen and other U.S. maritime grievances against Britain. The U.S. Navy made an important contribution to the Union’s victory in the American Civil War (1861–65) by mounting a blockade of Confederate seaports. The navy won easy victories over Spanish fleets in the Spanish-American War (1898), and over the next two decades it grew steadily in power and efficiency. Naval aviation was inaugurated in 1910 when a civilian pilot, Eugene Ely, flew an airplane off a cruiser at Hampton Roads, Virginia; the next year he landed on and took off from a cruiser in San Francisco Bay. The Office of the Chief of Naval Operations was set up in 1915, and an important shipbuilding program was begun in 1916.

Although the U.S. Navy did not engage in sea battles during World War I, it nevertheless grew eightfold in size. Its chief activities were the transport of about 2,000,000 U.S. troops to France, the patrolling of the North Atlantic sea lanes to protect Allied commerce shipping from German U-boats, and the laying of a large antisubmarine minefield in the North Sea. During the interwar years, the first U.S. aircraft carrier, the USS Langley, was launched (1922), a naval patrol was placed in the Atlantic (1939), and the escort of Allied convoys was begun (1941).

The United States entered World War II after the Japanese attack on the U.S. naval base at Pearl Harbor, Hawaii, on December 7, 1941. During the war the U.S. Navy undertook a huge building program that made it larger than all the other combatant nations’ navies combined. It expanded from a force of about 300,000 officers and men in mid-1941 to more than 3,000,000 by war’s end. The navy played a more important role in American military operations during World War II than in any previous war in the nation’s history. In addition to antisubmarine operations and troop transport duties, it conducted several major series of amphibious assaults in the Pacific theatre and along the European coast, for which it developed new landing craft and tactics. U.S. naval forces fought many major battles with Japanese forces in the Pacific in which aircraft carriers proved decisive. Aircraft carriers have since formed the backbone of the U.S. Navy’s fleets.

Since World War II the U.S. Navy has remained the largest and most powerful navy in the world. It built the Nautilus (1954), the world’s first nuclear-powered submarine, and the Enterprise (1961), the first nuclear-powered aircraft carrier. The navy went on to build a fleet of nuclear-powered submarines that served as underwater launching platforms for intercontinental ballistic missiles armed with nuclear warheads. These submarine-launched ballistic missiles became an important component in the United States’s strategic-deterrence forces. The navy also led in adapting cruisers and submarines for the firing of tactical guided missiles.

The Department of the Navy was placed within the Department of Defense by the 1949 amendments to the National Security Act of 1947. The navy includes the U.S. Marine Corps and, during wartime, the U.S. Coast Guard. The department is headed by a civilian secretary of the navy, who is appointed by the president acting as commander in chief. The chief of naval operations, the senior military officer, advises the president and the secretary, is a member of the Joint Chiefs of Staff, is commander of the navy’s operating forces (except the Marine Corps), and directs the Naval Reserve.

The U.S. Navy’s four operating forces are the Pacific Fleet, which operates in the Pacific and Indian oceans; the Atlantic Fleet, which operates in the Atlantic Ocean and the Mediterranean Sea; the Naval Forces, Europe; and the Naval Forces, Central Command, which operates in the Middle East. In addition to its four operating forces, the navy’s Military Sealift Command provides ocean transport on government or commercial vessels for the Department of Defense and other federal agencies, provides at-sea logistic support to the armed forces, and conducts scientific and other projects for federal agencies.

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